1. Field of the Invention
The subject matter of the present invention concerns Continuously Variable Transmissions (CVT's), generally. More specifically, the invention is related to the torque responsive pulley of a Continuously Variable Transmission system. More specifically, the present invention is related to the cam assembly and roller of the torque responsive pulley of a Continuously Variable Transmission system.
2. Description of the Prior Art
The torque responsive pulley, hereinafter the driven pulley, of a Continuously Variable Transmission, hereinafter CVT, has an inner conical-shaped or progressive angled sheave 40 (also known as the moveable sheave) and an outer conical-shaped or progressive angled sheave 42 (also known as the fixed sheave), as shown in FIG. 3A. The inner and outer sheaves 40, 42 are biased toward each other such that the conical faces 64 and 58 of each sheave are facing each other. The biasing member is a spring 44. For simplicity, reference is made to FIG. 3A showing the cam 20 and roller assembly 22 of the present invention. The remainder of the components shown in FIG. 3 are well known parts of a CVT driven pulley. The conventional driven pulley also comprises a torque sensing device or cam of the types shown in FIGS. 1 and 2 having two sets of cam surfaces, one for clockwise application of torque and one for counterclockwise application of torque. The cam surfaces are angled to provide a ramp or helices over which a slider or roller will contact the surfaces and force the inner sheave away from the outer sheave as the torque load on the driven pulley increases. In a roller-type driven pulley, the cam surfaces are basically a single slope or angled slots within the cam. Each slot provides one surface for the roller during clockwise application of torque of the driven pulley and an opposing surface for the roller during counterclockwise application of torque of the driven pulley. The roller will also contact each surface when the torque transmitted to driven pulley is inverted. Such an example of a roller-type cam can be seen in U.S. Pat. No. 6,120,399. Referring to the '399 patent, torque applied to a driven shaft is communicated by the spider 26 to the motion-producing closed cam 28 that has a diametrically opposed pair of sloped first (inner) cam surfaces 64 spaced-apart from a corresponding pair of diametrically opposed pair of sloped second (outer) cam surfaces 66. A roller 68 fits between each of the corresponding first cam surfaces 64 and second cam surfaces 66. The rollers 68 rotate on a pair of diametrically opposed roller shafts 70. Rollers are secured to the roller shafts 70 by a suitable C-ring, pin, clip or other roller fastener 72.
In certain applications, CVT's are used with engines where the output shaft can rotate in two directions. In these applications, the cam has to be modified to allow the rollers to have sufficient contact surface during initial engagement between the roller and the cam when in the reverse mode. Cam 2, shown in FIG. 1, is suited for reverse operation and thus it has cam surfaces 6 which make contact with the slider during reverse torque operation. In certain CVT applications, it is also known to use these surfaces for engine braking.
Cam 10, shown in FIG. 2, is another example of a prior art cam, which is suitable to be used in a reverse direction. Cams 2 and 10, as shown in FIGS. 1 and 2, have large circumerential distances between opposed cam surfaces 4 and 6 or 12 and 14 thus allowing the pulley sheaves to be forced toward the fully closed position during a change in direction of torque transmitted to the driven pulley. Also, with reference to FIGS. 1 and 2, cams 2 and 10 have no means to prevent the roller or slider from traveling toward the fully opened position when the sheaves are approximately in a fully closed position, i.e. to lock the roller or slider in a certain position between the fully closed and fully opened positions. In both cases, since the cam cannot offer sufficient support to the roller, the transmission is forced into a higher gear ratio than would be optimal for maximum power transmission to the ground engaging tracks or wheels.
A need has therefore arisen for an improved driven-pulley cam and roller therefor.